Drilling pipe is ready for use at SAWS' Drill Site No. 2 in South Bexar County next to Wilson County. The well will pump saltwater, which will be piped to a treatment plant, treated and then used in San Antonio. Tuesday, March 27, 2012.

Photo By BOB OWEN/San Antonio Express-News

SAWS chairman Heriberto Guerra Jr. dedicates a saltwater well in southern Bexar County on Tuesday, March 27, 2012. Water from the well will be piped to a treatment plant.

The San Antonio Water System is now pumping saltwater in southern Bexar County as it looks for new water sources for the city.

On Tuesday the utility gave a tour of one of its first production wells in the middle of a pasture that will tap the lower Wilcox Aquifer.

Because it is an expensive new project going after a new source, it will be watched closely by residents for possible impact on local water supplies and by state officials for its potential to set an example of a new water source for Texas.

The $145 million project is expected to produce 10 million gallons a day by 2016, when the desalination plant and pipelines are complete. That's about 5 percent of San Antonio's daily demand, according to SAWS.

“Here is the goal,” said Mayor Julián Castro, who supports the project. “There should never be a question that San Antonio does not have the water it needs to thrive.”

By sinking 13 wells 1,500 feet into the sand below southern Bexar County, the public utility can pull up the unregulated, brackish water.

Previous attempts to get that water out of Wilson and Atascosa counties was met with fierce local opposition; so SAWS opted to locate the wells in southern Bexar, where there is no groundwater district.

The wells will still draw water from below all three counties, but SAWS will leave the local freshwater in the Carrizo Aquifer, which lies above the Wilcox Aquifer in Atascosa and Wilson counties, SAWS CEO Robert Puente said.

“That freshwater should stay for local use,” he said.

At about half the salinity of seawater, the water of the lower Wilcox is too salty for use in irrigation and until now has been left alone. But through reverse osmosis treatment, salt-free water can be extracted, SAWS staff members said.

The remaining water, which is left with a much higher concentration of salt, is injected into the brackish portion of the Edwards Aquifer. In southern Bexar, that formation is about 4,000 feet below the surface.

The cost of treating and then pumping the water uphill to San Antonio makes it cost about five times as much as water from the Edwards Aquifer.

For Wilson County Judge Marvin Quinney, the SAWS project is good, because it taps water his county can't access due to the cost of the treatment. He also sees less chance of contamination of his county's freshwater with the SAWS wells located in Bexar.

“Test it in Bexar County first,” he said. “Be honest with the results.”

If the first phase goes as planned, SAWS anticipates expanding the project to 25 million gallons a day by 2026.

The water in the Wilcox is believed to be a combination of water left over from the time when South Texas was under a shallow sea and includes some very slow infiltration of rainwater from the surface.

In various aquifers across Texas, the state estimates there are 2.7 billion acre-feet of such water, said Weir Labatt, who sits on the Texas Water Development Board.

That's enough to cover all of Texas with more than 15 feet of water.

“What you are really doing is mining it,” Labatt said. “But it's there, so you might as well use it.”